A. Epicardium - outermost, = Visceral layer of the serous pericardium
B. Myocardium - middle, = Cardiac muscle cells (very thick)
The Heart Wall
C. Endocardium - innermost, forms valves, & is continuous with the endothelium of the blood vessels that enter & leave the heart
2 upper: Lt. & Rt. Atrium
2 lower: Lt. & Rt. Ventricle
2 Atrioventricular (AV) Valves
Rt. AV valve = tricuspid
Lt. AV valve = bicuspid, mitral
2 semilunar valves: found at the base of 2 large vessels leaving the heart = Pulmonary & Aortic valves
1. Rt. Atrium: receives deoxygenated (venous) blood from 3 vessels;
A. Superior vena cava - blood from above the heart
B. Inferior vena cava - blood from below the heart
C. Coronary sinus - blood from the heart muscle
2. Blood flows through Rt. AV valve into Rt. Ventricle (the flaps of AV valves are held in place by Chordae Tendineae & Papillary Muscles to prevent back flow)
3. Rt. Ventricle contracts & blood exits through the Pulmonary Semilunar valve. It enters the Pulmonary trunk which divides into Lt. & Rt. Pulmonary arteries. Blood goes to lungs (carbon dioxide out, oxygen in)
Blood Flow cont.
4. Oxygenated blood returns from the lungs through the Pulmonary veins to the Lt. Atrium
5. Blood flows through the Lt. AV valve (bicuspid, mitral) to the Lt. Ventricle
6. Lt. Ventricle contracts & blood exits through the Aortic Semilunar valve & enters Ascending Aorta.
Coronary circulation (Blood flow to Heart Muscle)
First vessels off of the Ascending Aorta = Lt. & Rt. Coronary Arteries
Coronary Circulation cont.
The blood returns from the heart muscle via 2 major veins
1. Great Cardiac vein: brings deoxygenated blood back from the anterior heart wall
2. Middle Cardiac vein: brings deoxygenated blood back from the posterior heart wall.
Both vessels empty into the Coronary Sinus (a large vein on back of heart). It empties into Rt. Atrium
An electrical system. It determines the rate & rhythm of the heartbeat
1. Sinoatrial node (SA node, pacemaker) - Neurons fire at 70/80 beats per minute, causes atria to contract
2. Atrioventricular node (AV node) - neurons fire at 40-50 beats per minute; typically the SA node overrides it, but if SA node is not functioning it will ultimately cause ventricles to contract at a slower rate.
3. Atrioventricular Bundle (Bundle of His) - conducts impulses between ventricles
4. The AV Bundle divides into lt & rt Bundle Branches which go to the ventricles.
5. Purkinje fibers - deliver impulses directly to the myocardium of the ventricles .
Blood – connective tissue with fluid matrix
A. Fluid = plasma
B. Blood cells = formed elements
1. Red blood cells (RBC's) = ERYTHROCYTES
a. Flattened, biconcave, anucleated discs
b. Life span - 120 days
c. Function: transport oxygen & carbon dioxide bound pigmented protein = hemoglobin
2. White blood cells (WBC's) = LEUKOCYTES
2. White blood cells (WBC's) = LEUKOCYTES
3. Thrombocytes = PLATELETS; not cells. Cytoplasmic fragments of megakaryocytes. Assists in blood clot formation.
Hemopoiesis = Blood Cell formation. Occurs in red bone marrow.
A. Erythropoiesis = RBC formation
B. Leukopoiesis = WBC formation
C. Thrombopoiesis = platelet formation
Blood vessels: blood flow
Blood flows from the heart through progressively narrowing vessels; artery ->arteriole -> capillary
And returns through progressively enlarging vessels;
venules -> vein-> heart
Structure: arteries and veins have 3 tunics
1. Tunica Externa (adventitia) - Outermost, loose connective tissue, this is the thickest layer in veins
2. Tunica Media - middle, smooth muscle layer, this is the thickest layer in arteries
3. Tunica Intima - innermost
a. Endothelium - simple squamous + c.t.
b. Subendothelial layer - c.t.
Arteries (carry blood away from heart)
Elastic - large amount of elastin expandable
Muscular - tunica media is predominantly smooth muscle.
There is an elastic lamina on each face of the tunica media
Smallest, tunica media very thin (<10 layers)
"Functional units" of circulatory system, very thin-walled, allows for exchange of gases, nutrients, & waste products.
Composed of the Tunica Intima only
Usually lack a tunica media. They have the other two tunics
Carry blood to the heart) All 3 tunics present. Veins have a very
Low pressure, The blood flow through them is dependent on:
A. Contraction of surrounding musculature = Skeletal muscle "pump"